Apparatus for shock deformation of workpieces

ABSTRACT

An apparatus for shock deformation of workpieces comprises a pressure chamber surrounded by at least two walls and arranged to accommodate a workpiece and a die as a surface contour which is to be imparted to the workpiece by shock deformation of the latter into conformance with the surface contour. The walls have respective juxtaposed surfaces and at least one of the walls is movable relative to the other between a chamber-closing position in which the surfaces abut in other-than fluidtight contact and a chamber-opening position. The walls has an inertia so selected as to at least substantially equal the shock pressure necessary for producing the energy level required to obtain the desired deformation of the workpiece so that upon exceeding of the necessary shock pressure relative movement of the walls to the chamber-opening position results with concomitant venting of the chamber. Shock pressure producing means produces a sudden increase in pressure in the chamber. A quantity of pressuretransmitting liquid fills the pressure chamber to a predetermined level and is operative for transmitting shock pressure to the workpiece. Portions of the liquid tends to escape from the chamber between the surfaces so that the level of liquid tends to drop. Replenishing means replenishes the quantity of liquid in the pressure chamber to thereby maintain the predetermined level at least substantially steady.

White tats Hertell et all.

atet

[ Feb. 22, T1972 Primary Examiner-Richard J. ll lerbst Att0rneyMichael S. Striker [72] Inventors: Heinrich lilertel, Tannenbergallee 36, Ber- [57] ABSTCT lin 19; Dietrich Ruppin, Berlin, both of Germany An apparatus for shock deformation of workpieces comprises a pressure chamber surrounded by at least two walls and ar- [73] Asslgnee' Sam Heme, by Sam Rum! ranged to accommodate a workpiece and a die as a surface 22 Fil d; g 24, 19 9 contour which is to be imparted to the workpiece by shock deformation of the latter into conformance with the surface [211 APPL1\]'1 $69,704 contour. The walls have respective juxtaposed surfaces and at least one of the walls is movable relative to the other between 30] Foreign A li ti M n n w a chamberclosing position in which the surfaces abut in other-than fluidtight contact and a chamber-opening position. Sept 1968 Germany 17 208-6 The walls has an inertia so selected as to at least substantially equal the shock pressure necessary for producing the energy [52] "72/56 level required to obtain the desired deformation of the work- [51] i a 26/08 piece so that upon exceeding of the necessary shock pressure 0% Search E relative movement of the walls to the chamber opening p 56 R f d tion results with concomitant venting of the chamber. Shock 1 Memes We pressure producing means produces a sudden increase in pres- UNITED STATES PATENTS sure in the chamber. A quantity of pressure-transmitting liquid fills the pressure chamber to a predetermined level and IS 2,935,038 1960 h r!" operative for transmitting shock pressure to the workpiece. 3,149,372 1964 s Portions of the liquid tends to escape from the chamber 3, l 1965 Nemlil between the surfaces so that the level of liquid tends to drop. 3,232,085 2/1966 lnoue ..72/5 Replenishing means replenishes the quantity of liquid in the 3,267,710 8/1966 lnoue ..72/56 pressure chamber to thereby maintain the predetermined |evel 3,273,365 9/1966 Felts ..72/56 at least Substantially steady 3,376,723 4/1968 Chelminski ..72/56 1122 Claims, 3 Drawing Figures PMENIEIJFEB22 m2 3., M3 0482 SHEET 1 OF 2 had M I PATENTEDFEB 22 I972 3v 6 ,4 8 2 sum 2 BF 2 INVENTORS ATTORNEY APPARATUS FOR SlhllOtClli DEEDRMATHUN GT" WURIIQPTIECIES BACKGROUND OF THE INVENTION The present invention relates generally to a device for shock-deformation of workpieces, and more particularly to such a device which has a self-venting pressure chamber.

It is already known to deform workpieces by submitting them to sudden shock, for instance by setting off explosives or by using analogous means. it is also known to utilize self-venting pressure chambers in such devices, that is pressure chambers wherein one or more walls move to a position in which the pressure chamber is opened when the pressure in the chamber reaches and exceeds a predetermined level. The means for maintaining the movable wall or walls in closed position against the developing pressure-until the latter reaches the predetermined level-usually requires significant structural and technological expenditures because of the forces to be restrained.

German Pat. No. 1,259,825 teaches a construction intended to simplify devices of the type in question and wherein the pressure chamber is bounded by a stationary and movable walls, with the mass of the movable walls being so selected that the developing pressure in the interior of the pressure chamber is largely counteracteduntil it reaches the predetermined level at which venting is desired-by the inertia of the masses. This is evidently a significant improvement over the prior art construction.

However, it has been found that it is difficult in this device to seal the pressure chamber against the escape of the pressure-transmitting liquid which is contained in the interior of the pressure chamber and which serves to transmit the shock pressure to the workpiece, the latter also being located in the pressure chamber. Of course, an obvious approach to the problem is to provide sealing elements, such as rubber O-rings or analogous means on the abutting surfaces of the relatively movable walls of the device. This has not, however, found to be a satisfactory solution because the pressure-transmitting liquid is ejected with high kinetic energy from the interior of the pressure chamber when the movable walls move to chamber-opening position to vent the interior of the chamber, and this frequently results in damage to the sealing element. Thus, sealing elements provided in such devices have not had a satisfactory life and have had to be replaced too frequently for this type of sealing to be acceptable. Evidently, frequent replacement with concomitant downtime of the device adversely influences the economy of the operation.

SUMMARY OF THE llNVENTlON it is, accordingly, a general object of the present invention to provide an improved device of the type under discussion.

More particularly, it is an object of the present invention to provide such a shock-deformation device which is not possessed of the aforementioned disadvantages.

Still more specifically, it is an object of the present invention to provide such a device wherein the necessary and the desired level of pressure-transmitted liquid into the interior of the pressure chamber is maintained without sealing the chamber in any manner.

In pursuance of the above objects, and others which will become apparent hereafter, one feature of the invention resides in an apparatus for shock deformation of workpieces which comprises, and briefly stated, wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to the workpiece by shock deformation of the latter into conformance with the surface contour. The wall means include at least two walls having respective juxtaposed surfaces, and at least one of these walls is movable relative to the other between a chamber-closing position in which the surfaces abut each other with what is, according to the invention, other-than fluidtight contact, and a chamber-opening position. The wall means has an inertia so selected as to at least substantially equal the necessary shock pressure for producing the predetermined energy level requisite to obtain the desired deformation of the workpiece so that upon exceeding of this shock-pressure relative movement of the walls to chamberopening position results with concomitant venting of the chamber. Shock-pressure producing means is provided for producing a sudden increase in pressure in the chamber. A quantity of pressure-transmitting liquid fills the pressure chamber to a predetermined level in known manner and serves for transmitting shock pressure to the workpiece. Because, in accordance with the invention, no seal is provided between the abutting surfaces, portions of the liquid tend to escape from the chamber between the surfaces so that the level of liquid tends to drop. According to the invention, there is further provided replenishing means for replenishing the quantity of liquid into the pressure chamber to thereby maintain the predetermined level of liquid in the pressure chamber at least substantially steady.

The quantity of liquid which tends to escape, or actually does escape, between the abutting surfaces of the relatively movable walls, is relatively small and continuous replenishing of the liquid in the interior of the pressure chamber readily enables the maintenance of the predetermined liquid level.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construc tion and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRllEF DESCRlPTlON OF THE DRAWING H6. 1 is a vertical, diagrammatic section through an apparatus according to the present invention, illustrating one inventive embodiment;

FIG. 2; is a view similar to FIG. l but illustrating a further embodiment of the invention; and

MG. 3 is also a view similar to FIG. l but illustrating yet another embodiment of the invention.

DESCRlPTlON OF THE PREFERRED EMBODIMENTS Discussing now the drawing in detail, and firstly ElG. ll thereof, it will be seen that reference numerals ii and 2 identify wall means of suitable configuration, for instance that shown in MG. l, which hereafter will be identified as the upper mass 1 and the lower mass 2.. Such wall means, the manner in which it defines the pressure chamber 117, and the manner in which the closing of the pressure chamber as a result of so selecting the masses it and 2 that their inner share is capable of withstanding the shock pressure to the desired extent, is known from the aforementioned German Pat. No. 1,259,825.

The masses it and 2 are mounted and guided for relative movement in vertical direction by the guide rods 3, guide means l being provided which movably connect the mass gun with the guide rods 3, and guide means 5 serving the same purpose with reference to the mass 2. The latter is further supported by two or more springs b which are of course so constructed and dimensioned as to be able to support the masses 11 and 2, and to restore the mass 2 to the illustrated rest position of PEG. 1 after it has been downwardly displaced-with concomitant upward displacement of mass ll-during venting of the chamber T7. The guides 4i and 5, as well as the springs t}, are illustrated diagrammatically because they do not in themselves constitute a part of the present invention and need to be shown only to facilitate a description of the operation of the device.

As HG. ll shows, the components described thus far are surrounded by and accommodated in a reservoir 6 containing a body 7 of pressure-transmitting liquid, with more of this liquid being accommodated in the interior of the chamber 117 to a predetermined level, in the illustrated embodiment, completely filling the chamber 317.

U... lMlE There is further provided a suction conduit extending into the body of liquid 7, a pressure conduit 11 extending into the interior of the pressure chamber 17 and being guided in the mass 2 in such a manner that the latter is capable of performing its movements lengthwise of the supports 3 and with reference to the conduit ill, and a pump interposed between the conduits 10 and 11 serving to draw liquid from the body 7 and pump it into the interior of the pressure chamber 17. A supporting device 12 of suitable construction supports the pump 9 as well as the conduits 10 and 12 in the interior of the receptacle 6. The latter, it will appreciated, serves as a support means for the remaining components. Mounted in the upper mass 1 is shock-pressure producing means 13, for instance in form of a cartridge containing gun powder, an actuating mechanism 14 which, if the charge E3 is gun powder, serves to ignite it, and a venting bore 15. Of course, the recess in which the charge 13 is located communicates with the interior of the chamber 17.

When the device is not in operative position, that is when the pressure chamber 17 is not filled with liquid, all of the liquid is contained in the reservoir 6. The liquid may be water, oil, or another suitable medium. For the device to be operated, the masses 1 and 2 are separated, the die 18 is introduced into the pressure chamber 17, unless it is already present, and a workpiece 16 which is to be deformed is placed onto the die. In the illustrated embodiment, the die has a recessed surface contour so as to define with the workpiece the space 10. Sealing means 19 seals the juncture between the surface of the workpiece and the surface of the die, and the space 20 can thus be evacuated via an evacuating conduit 21 which is connected in suitable manner with a source of underpressure. Of course, the die could have another configuration or it could be provided simply by forming the desired surface contour in the surface of the mass 2 which faces the interior of the pressure chamber 17. In any case, after the die and workpiece have been introduced and, where the space 20 exists, the space 20 has been exhausted, the masses l and 2 are moved into abutting engagement of the juxtaposed surfaces, as illustrated in FIG. 1. Now the pump 9 is started which continuously draws liquid from the body 7 and introduces it into' the interior of the pressure chamber 17. As the pressure chamber 17 fills, liquid escapes at the interface 22 of the abutting surfaces of the masses 1 and 2, because no seal is provided at this interface. However, the quantities of liquid which so escape are small enough so that they are continuously replenished by additional liquid which is forced into the pressure chamber 17 by the pump 9. Venting conduit 15 of course serves to vent the pressure chamber when the liquid is initially introduced.

The pump 9 is advantageously adjustable, but in any case its capacity will be so selected that the pump is capable of replenishing losses occuring at the interface 22 as well as through the venting bore 15, so that in the illustrated embodiment the entire pressure chamber l7 will be constantly filled with liquid.

Subsequent to triggering of the charge 13 and explosive deformation of the workpiece 16, the peak pressure will move the masses 1 and 2 apart, and the pressure 17 is vented by the escaping gases and the liquid. Now the workpiece is removed and replaced with a new blank.

The embodiment illustrated in FIG. 2 differs from that of FIG. 1 in that the guide rods 3 are here connected with the lifting devices 23 which may, for instance, be hydraulic cylinders or the like. The connection between the devices 23 and guide rods 3 is such that by means of the abutments 24 and 25 provided on the guide rods 3', the masses 1 and 2 can be lifted above the level of liquid 26 contained in the reservoir 6. How this is accomplished is readily evident, but it is emphasized that the arrangement of the abutments 24 and 25 with reference to the guides of the masses 1 and 2 against which they abut, is so selected that as the masses 1 and 2 are lifted in upward direction, they are also separated so that the interior of the pressure chamber is opened, the liquid in the pressure chamber 17 will run off and the deformed workpiece will be readily available for withdrawal and replacement with a new blank. The workpiece is again identified with reference numeral 1 .6, the die with reference numeral 18, the venting bore with reference numeral 15, and the space between the workpiece and the surface of the die with reference numeral 20. Reference numeral 21 is again the evacuating conduit and reference numeral 23 identifies the flexible conduit or hose communicating with the conduit 21, for constituting a flexible portion thereof, to permit evacuation of the space 20.

Insertion or removal of workpieces can be accomplished via the sliding door 30.

In the operative position of the device in FIG. 2, the masses 1 and 2 are immersed in the body of liquid 7 contained in the reservoir 6, as illustrated. The latter, incidentally, in this embodiment constitutes again a supporting or mounting arrangement for the masses 1 and 2 of the associated components.

In conduits or passages 27here provided in the mass 1 and communicating with the interior of the chamber 17serve to fill the chamber 17 with liquid under simultaneous expulsion of air through the venting conduit 15 when the masses 1 and 2 are introduced into the body of liquid 7 as shown in FIG. 2.

Coming, finally, to the embodiment illustrated in FIG. 3, it will be seen that this differs from the preceding embodiment primarily in the construction of the reservoir 6". The latter here is subdivided into three separate compartments 34,35 and 36, which communicate with one another through apertures arranged in the region of the respective bottom of each compartment and closable by the valves 33. Because of the communication of these compartments 34,35 and 36, the level of liquid-the body of liquid 7is the same in all three compartments. When the device is thus introduced into the container 6", the pressure chamber 17 is filled with pressuretransmitting liquid by means of the filling channels 27. As a comparison between the liquid levels in the chamber 17 and exterion'ly thereof indicates, a small quantity of pressuretransmitting liquid will be accommodated in the lower end portion of the venting conduit 15.

After the device has been operated with reference to the embodiments of FIGS. 1 and 2, the pressure-transmitting liquid is drawn out of the chamber 36 by the pumps 31 into and transferred into the chambers 34 and 35 so that in these it rises to a level higher than that in the chamber 36. Of course, the valves 33 are closed at that time. Similarly, the one-way valves 32 prevent return flow of liquid through the conduits associated with the pump 31. This permits ready access to the apparatus in the compartment 36, so that the deformed workpiece may be removed, a new one put in place and a new charge installed. Subsequently, the pumps 31 are stopped, and the valves 33 are opened so that the liquid level of all three compartments 34,35 and 36 becomes again equalized whereby the device is ready for the next operation.

Aside from the already discussed advantages which permit in constructions according to the present invention the elimination of separate sealing means, the embodiments in FIGS. 2 and 3 provide the additional advantages which will already be evident from their description and from a consideration of FIGS. 2 and 3. Summarized, it may be pointed out that in these embodiments the liquid which surrounds the structural elements, which in turn define the internal pressure chamber 17 provides a significant support factor for the material of the structural elements so that the latter do not have to withstand as high stresses during the triggering of the charge which would otherwise be necessary. Furthermore, the liquid serves to dampen the movements of the movable components, thereby on the one hand decreasing the size of the movements performed and making it possible to construct a device which is lower than would otherwise be feasible, and on the other hand eliminating the necessity for separate damping devices.

Because the liquid surrounds the pressure chamber 17 during the operation of the device, the noise factor is greatly reduced, particularly in the high frequencies which are 'especially objectionable. Finally, the fact that pressure-transmitting liquid is present eirteriorly of the chamber when the same is vented, resists the ejection of liquid from the interior of the chamber and thus makes possible an increase in the ef fectiveness of the device by approximately percent.

The embodiments illustrated in FlGS. l and ii are particularly advantageous for large-dimensioned constructions, because in these embodiments the loading plane remains unchanged and is not affected by the filling of the device with pressure-transmitting liquid. However, by providing suitable supports in the embodiment of lFlG. 2, the latter may also be constructed a larger dimensioned configuration.

The embodiment in H6. may be operated with a container having only two compartments, that is one of the compartments M or 35 may be omitted if desired, and if this is for instance necessary because of space limitations. Furthermore, if necessary the single remaining compartment dd or Bid, or both of the compartments Bid or 355, may be separated from the central compartment Elbaccommodating the apparatus may be located remote therefrom. in this case, suitable conduits connect the central compartment with the one or two other compartments. lf displacement bodies-which are not illustrated but which will be readily understandable to those skilled in the art-are provided which can be inserted into or withdrawn from the liquid in the compartments and 35 at will, are provided, then the pumps Elli may be omitted. The same is true if either the compartment 3b is movable relative to the compartments 3d and Fifi, or the latter are movable relative to the compartment Elti, in vertical direction, because in all of these instances, the level of liquid in the compartment 3b may be regulated without the necessity for the pumps Ell as will be evident to those skilled in the art.

As illustrated in lFlGS. 2B and it, the containers accommodating the apparatus and additional pressure-transmitting liquid 7 must have sufficient free airspace above the liquid level to prevent excessively strong transmittal of pressure from the apparatus through the pressure-transmitting liquid eirteriorly of the apparatus into the walls of the containers. For the same purpose there is provided the element Ilti shown in H6. El which may for instance be a gas-tilled of elastically deflectable material and which has an analogous function as residual airspace above the level of the liquid in the container 6". in fact, the element 2d may be so constructed as to replace the springs 8 (compare lFlG. ll) if desired. Finally, it is emphasized that the lower movable mass 2 itself may have the surface contour to which the, that is the lower movable mass 2 may at the same time serve as a die without requiring the provision of a separate die as in FIGS. l and 2. Of course, this possibility exists also in H65. 11 and 2 where the dies may be omitted and the construction may be the same as in FlG. ft with reference to the provision of the die.

it will be understood that each of the elements described above, or two or more together, may also find a useful applica tion in other types of constructions differing from the types described above.

While the invention has been illustrated and described as embodied in an apparatus for shock deformation of workpieces, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

What is claimed is:

l. Apparatus for shock deformation of workpieces, comprising wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to said workpiece by shock deformation of the latter into conformance with said surface contour, said wall means including at least an upper and a lower wall having respective juxtaposed surfaces, said walls being movable relative to each other between a chamber-closing position in which said surfaces abut in other-than tluidtight contact and a chamber-opening position, and said wall means having an inertia so selected as to at least substantially equal the necessary shock pressure for producing the predetermined energy level requisite to obtain the desired deformation of said workpiece so that upon exceeding of said necessary shockpressure relative movement of said walls to said chamberopening position results with concomitant venting of said chamber; guide means mounting said upper wall for vertical movement relative to said lower walL; elastic supporting means elastically supporting said lower wall; shock-pressure producing means for producing a sudden increase in pressure in said chamber; a quantity of pressure-transmitting liquid filling said pressure chamber to a predetermined level and being operative for transmitting shock pressure to said workpiece, portions of said liquid tending to escape from said chamber between said surfaces so that the level of liquid tends to drop; and replenishing means for returning said portions into said chamber so as to replenish the quantity of liquid in said pressure chamber to thereby maintain said predetermined level at least substantially steady.

2. Apparatus as defined in claim ll, said replenishing means comprising a reservoir for collecting escaping liquid, conduit means connecting said reservoir with said pressure chamber, and circulating means for recirculating the collected liquid to said pressure chamber.

3i. Apparatus as defined in claim ll, said replenishing means comprising a reservoir containing a body of said pressuretransmitting liquid, and supporting means supporting said wall means in said body of liquid with said chamber communicating with said body of liquid, and at a depth requisite for maintaining said predetermined level of liquid in said chamber.

d. Apparatus as defined in claim 3; and further comprising passage means communicating with said body and said pressure chamber.

5. Apparatus as defined in claim d, wherein said passage means comprises at least one aperture in said wail means.

6. Apparatus as defined in claim d, wherein said passage means comprises the interface between said surfaces.

7. Apparatus as defined in claim 2, wherein said reservoir is connected with and constitutes a structural support for said wall means.

Apparatus as defined in claim )1; and further comprising a gas-tilled elastically yieldable element accommodated in said body of fluid for absorbing shock pressure originating in said chamber in response to operation of said shock-pressure producing means.

Apparatus m defined in claim 3; and further comprising liquid-displacement means, and moving means for moving said liquid-displacement means into and out of said body of liquid in said reservoir to thereby vary the level of said body of liquid directly, and said predetermined level indirectly.

it). Apparatus as defined in claim 3; and mounting means mounting said reservoir for at least substantially vertical displacement relative to said wall means for directly varying the level of said body of liquid relative to said predetermined level, and to thereby indirectly vary said predetermined level.

llll. Apparatus as defined in claim El, said reservoir comprising at least two laterally adjacent compartments each having a lower region, said compartments communicating with one another in their respective lower regions and said wall means being accommodated in one of said compartments.

till. Apparatus as defined in claim i2; further comprising at least one aperture connecting said compartments for communication with one another, valve means for opening and closing said aperture, conduit means communicating with both of said compartments, and pump means for pumping liquid from said one compartment through said conduit into the other of said compartment for varying the relative levels of liquid in said compartments when said valve means closes said aperture. 

1. Apparatus for shock deformation of workpieces, comprising wall means surrounding a pressure chamber arranged to accommodate a workpiece and a die having a surface contour which is to be imparted to said workpiece by shock deformation of the latter into conformance with said surface contour, said wall means including at least an upper and a lower wall having respective juxtaposed surfaces, said walls being movable relative to each other between a chamber-closing position in which said surfaces abut in other-than fluidtight contact and a chamber-opening position, and said wall means having an inertia so selected as to at least substantially equal the necessary shock pressure for producing the predetermined energy level requisite to obtain the desired deformation of said workpiece so that upon exceeding of said necessary shock-pressure relative movement of said walls to said chamber-opening position results with concomitant venting of said chamber; guide means mounting said upper wall for vertical movement relative to said lower wall,; elastic supporting means elastically supporting said lower wall; shock-pressure producing means for producing a sudden increase in pressure in said chamber; a quantity of pressure-transmitting liquid filling said pressure chamber to a predetermined level and being operative for transmitting shock pressure to said workpiece, portions of said liquid tending to escape from said chamber between said surfaces so that the level of liquid tends to drop; and replenishing means for returning said portions into said chamber so as to replenish the quantity of liquid in said pressure chamber to thereby maintain said predeterMined level at least substantially steady.
 2. Apparatus as defined in claim 1, said replenishing means comprising a reservoir for collecting escaping liquid, conduit means connecting said reservoir with said pressure chamber, and circulating means for recirculating the collected liquid to said pressure chamber.
 3. Apparatus as defined in claim 1, said replenishing means comprising a reservoir containing a body of said pressure-transmitting liquid, and supporting means supporting said wall means in said body of liquid with said chamber communicating with said body of liquid, and at a depth requisite for maintaining said predetermined level of liquid in said chamber.
 4. Apparatus as defined in claim 3; and further comprising passage means communicating with said body and said pressure chamber.
 5. Apparatus as defined in claim 4, wherein said passage means comprises at least one aperture in said wall means.
 6. Apparatus as defined in claim 4, wherein said passage means comprises the interface between said surfaces.
 7. Apparatus as defined in claim 2, wherein said reservoir is connected with and constitutes a structural support for said wall means.
 8. Apparatus as defined in claim 1; and further comprising a gas-filled elastically yieldable element accommodated in said body of fluid for absorbing shock pressure originating in said chamber in response to operation of said shock-pressure producing means.
 9. Apparatus as defined in claim 3; and further comprising liquid-displacement means, and moving means for moving said liquid-displacement means into and out of said body of liquid in said reservoir to thereby vary the level of said body of liquid directly, and said predetermined level indirectly.
 10. Apparatus as defined in claim 3; and mounting means mounting said reservoir for at least substantially vertical displacement relative to said wall means for directly varying the level of said body of liquid relative to said predetermined level, and to thereby indirectly vary said predetermined level.
 11. Apparatus as defined in claim 3, said reservoir comprising at least two laterally adjacent compartments each having a lower region, said compartments communicating with one another in their respective lower regions and said wall means being accommodated in one of said compartments.
 12. Apparatus as defined in claim 12; further comprising at least one aperture connecting said compartments for communication with one another, valve means for opening and closing said aperture, conduit means communicating with both of said compartments, and pump means for pumping liquid from said one compartment through said conduit into the other of said compartment for varying the relative levels of liquid in said compartments when said valve means closes said aperture. 